X = the number of similarly coloured socks strewn on the floor of your house before a friend comes to visit

Y = the number of socks that you are left with after they mix your generic black socks up with their own socks during packing or washing. The party who has the most illegitimate socks gains SOCK PROFIT.

Ben: Hey, there were 3 pairs of my black socks on the floor before you packed up, now there is 1!
Michael: ?!.....SOCK PROFIT!